ATM or asynchronous transfer mode is a data communications standard for allowing the delivery of data packets or frames to and from different network elements. An ATM network allows for the use and transfer of multiple types of data, e.g. constant bit rate, variable bit rate such as packets, video data, voice data, etc.
ATM transfers two types of Ethernet data. One type is bridged data or bridged frames. ATM bridged frames retain both the source and destination MAC address (Media Access Control), which may be a hardware address of a NIC (Network Interface Card) card in a PC. Thus, with bridged data, the source unit and destination unit are known. The other type of data is routed data or routed frames. Bridged data is used when a physical network is extended to include a larger number of network elements. Bridged data is viewed by all of the elements attached to the network. Routed data is used when a physical network is segmented, e.g. segmented geographically. The segmentation allows the data to be intelligently routed, i.e. routed to a specific device. The routed data is only viewed by the elements attached to the segment and not the entire network, if the routing is properly performed. Thus, system bandwidth is used more efficiently with routed data. A router selects a path based upon specific protocols and the destination address, and attempts to select the best or shortest path. Thus, the routers may strip the MAC headers off of the frames, and insert their own specific routing codes. Routers may be attached to an ATM network for the transmission of data. ATM uses a VPI (Virtual Path Identifier), and VCI (Virtual Channel Identifier), which together, make up a destination address, VP.VC.
The stripped headers cause problems during network analysis, particularly when the network analyzer software is designed to work with frames that have MAC headers. The exact source and destination MAC address of the routed frame may not be determined as the source information has been stripped out.
One prior art solution is to not reformat the data and just analyze the stripped frames. However, this approach results in a large reduction in the amount of LAN or WAN analysis that can be performed, particularly the lower layer analysis, as the source and destination of the data is not known. Thus, the MAC address layer would be lost, and the physical source and destination units could not be examined. Note that the lower layers would include physical and datalink layers, and the upper layers include network up through application layers. Since the data carried within the routed frame may include upper level addressing, e.g. TCP port or application address, then upper level analysis may take place.
Therefore, there is a need in the art for mechanism which allow network analysis software to operate on ATM systems using routed frames with MAC headers which have been stripped out, with the benefit of being able to tie upper layer analysis back to the lower layer ATM traffic carrying the data.
These and other objects, features and technical advantages are achieved by a system and method which allows routed frames to be analyzed by software that expects a MAC layer header.
The inventive mechanism is an interface which generates imitation MAC addresses and places the imitation addresses in the proper location, which is before the data portion of the frame. Thus, the software may perform analysis of the ATM network protocol layer and higher layers.
The imitation address is formed from useful information which will enhance the troubleshooting process of the analyzer software. The information would allow for upper layer protocol problems to be mapped down to lower layer ATM problems. The information must fill two addresses in order to create the imitation header which will be placed at the front of a routed frame, the source and the destination. Since ATM is destination based, the ATM destination address is encoded into the destination address of the imitation header. The port address upon which the data frame is captured is used as the source address of the imitation header. While this will not precisely identify the exact source of the frame, it will provide some intelligence as to its identity.
This invention will allow the use of existing software to do protocol analysis of routed ATM frames, and provide a link back to the ATM cells that carried the data. If for instance, the upper layer protocol analysis indicates a re-transmission at one of the upper layers, the encoded information would allow inspection of the cell layer and examination of data on the specific VP.VC to determine if the re-transmissions were the result of problems at the ATM layer, i.e. HEC errors.
Therefore, it is a technical advantage of the invention to allow network analyzer software which expects MAC protocols to operate with ATM routed frames.
It is a further technical advantage of the invention to generate imitation MAC headers from useful information which will improve the troubleshooting process of the network analyzer software.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.